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Studio di fattibilità per l’applicazione di tecnologie CCS su un ciclo combinato esistente

pubblicazioni - Articolo

Studio di fattibilità per l’applicazione di tecnologie CCS su un ciclo combinato esistente

feasibility study Luigi Mazzocchi*, Fabio Moia*, Michele Genova**, Gioia Usai**, Luca Derossi** Antonio Calabrò***, Stefano Consonni**** Quinta Conferenza sul mercato dei crediti di carbonio e sul Carbon Capture and Storage, all’interno di "Zero Emission Rome" Roma, 30 Settembre, 2 Ottobre 2009 PRESENTAZIONE POWER POINT ** CESI RICERCA ** TECHINT *** ENEA **** POLITECNICO MI The combined cycle that was taken into consideration is a plant of Techint group. It is composed by two gas turbines, fuelled by natural gas; the recovered heat is converted into steam, feeding a steam turbine. Some steam extractions from the turbine are used for cogeneration purposes, both for supplying heat to a steel factory and for district heating (DH). Nominal electrical power is about 120 MWe, while maximum heat provided is about 12 MWth for steel factory and 35 MWth for DH. Yearly CO 2 emissions are about 300 000 tons. Techint E&C, part of Techint Group who is the owner of the plant, decided to investigate the possibility to perform CO 2 capture, at least to some extent, in order to assess if this choice may become convenient, taking into account the European Emission Trading System (ETS). In particular, in the post-2012 period (3 rd period), it is expected that emission allowances will be decreased and, consequently, the cost per unit of emitted CO 2 could significantly increase. The project has been conceived as a modular one, so two different phases are envisaged. In the first phase, capture will be limited to about 45 % of the overall emissions. In this phase, the captured CO 2 is expected to be delivered to industrial users. Second phase will involve the capture of additional CO 2 quantities, up to a maximum of about 90 %. Taking into account the limited request of the Italian market, this additional CO 2 flow cannot be delivered to customers and should be stored underground. So, the study includes also some preliminary geological investigations. As far as capture is concerned, and considering that the most viable solution is a post-combustion process, the study took into consideration a number of alternatives, including the “classical” amine scrubbing with MEA, alternative solvents like Econamine SM Plus by Fluor, KS-1 SM by MHI, and Chilled Ammonia by Alstom. A complete technical and economic analysis was possible for the moment only for the MEA process, as the alternative solutions are not completely described in the available literature; however, the preliminary analyses performed in this phase showed the potential of significant improvements in terms of efficiency and energy cost. So, the results of this study are to be considered conservative; the alternatives will be reconsidered in a subsequent, more detailed analysis. In the MEA absorption/regeneration process, specific attention has been devoted to energy efficiency optimization, taking also into account the need to extract a large steam flowrate from the turbine, still allowing to satisfy the heat requirements of factory and district heating. As a matter of fact, results are in line with literature data and the overall estimated capture cost, of the order of 70 Euro/t CO2 , can be considered

reasonable if compared with equivalent data for coal fired power plants, that normally are expected to be less penalized by CO 2 capture. As far the final CO 2 disposal is concerned, the possibility to commercialize up to 30 % of the emitted CO 2 has been positively verified, and this is considered enough for phase 1 of the project. For phase 2, the quantity to be delivered to customers is too large, so a geological storage must be included. A preliminary geological analysis has been performed, showing that a suitable storage location is available at a reasonable distance (about 25 km) from the plant. A financial analysis was performed, taking into account the investment cost and energy penalty and, in term of benefits, primarly the saved emissions valorized according to the ETS system and the income from CO 2 commercialization; this last term could result important as it could potentially cover all the additional expenses for CO 2 capture. The actual price to be considered for the sold CO 2 depends essentially on the purity that will be achieved.

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